IPICS (IP Interoperability and Collaboration System), available from Cisco Systems, Inc., provides a means for rendering channels and virtual talk groups (VTGs) to endpoint devices (e.g. mobile communication devices), enabling users to participate in push-to-talk (P2T) communication. For simplicity of explanation, the term “channel” as used herein comprises both channels and virtual talk groups.
Push-to-talk communication is analogous in some respects to broadcast radio, e.g. FM radio stations. Whether or not an endpoint device can subscribe to (e.g. communicate with) a particular channel depends on the network topology, attachment of the endpoint to the network, network configuration, the configuration of endpoint device, and the configuration of the channel itself. Such channels are typically used by emergency services to broadcast information, and in contrast with the radio station (which usually transmits a signal continuously) the channel is often silent, e.g., in times when no communication is necessary. Thus, an end user often does not know whether silence indicates that he/she is listening to the channel but there is no current communication, whether he/she is not listing to the channel at all, or whether he/she is listening to a completely different channel.